Face milling is an efficient method for machining surfaces. One of the milling tools that can be used for face milling is the shank-end mill, which advantageously may be used for operations such as machining of shoulders, grooves and edges, and is constructed to give axial reach. By a greater axial reach, i.e., milling depth, more material can be removed in the same operation, which is economically advantageous. In the machining of small details, milling cutters of small diameters are needed. By small diameters, in this the text, a diameter of 25 mm and smaller is intended, foremost a diameter of 8-12 mm. Today, operators who need a milling cutter in the diameter range of 25 mm and smaller are reduced to using to either conventional solid shank-end mills provided with long helical cutting edges, or milling cutters having one or more detachably mounted milling inserts.
Solid milling cutters are often manufactured from high speed steel, cemented-carbide coated high speed steel, or from solid cemented carbide. A disadvantage of solid shank-end mills is that they have to be reground when they have become worn and thereby no longer can machine the material efficiently and precisely. The regrinding is often expensive since cemented carbide requires advanced grinding tools. Another disadvantage of regrinding of the tools is that a milling cutter, which from the beginning has had a certain diameter, intended for a specific operation, for instance a certain groove width, gets a reduced diameter after grinding. A more economic and practical solution is to use a milling tool having detachable milling inserts in which one or more milling inserts of cemented carbide machine the workpiece and then are replaced when they become worn. The milling inserts may be indexable, i.e., they may have a plurality of cutting edges, which further contributes to the economical advantage.
A shank-end mill provided with milling inserts has a higher machining capacity but is limited in the axial cutting depth by the length of the insert edge. Long insert edges entail that the milling insert becomes more sensitive to cutting forces, thereby running the risk of being dislodged from its position. During a milling operation, the milling insert will be subjected to great radial forces but moderate axial forces. These forces will act to displace and turn the milling insert, and it is therefore important to have a rigid clamping to avoid vibrations and that the milling insert tends to tip. By “tip”, it is here intended that the milling insert, because of forces acting on the cutting edge, turns out of its position. The number of milling inserts and the pitch vary depending on the diameter of the tool and which milling operation that is to be executed. A shank-end mill having indexable milling inserts may also be used for ramping operations, which is a combination of radial and axial feeding direction. A condition for ramping operations to be executable is, however, that the radial cutting depth of a pass does not exceed the insert width.
An indexable milling insert is usually clamped in a basic body by a center screw or the like fastening member. With decreased diameter of the tool, the milling inserts, and the screws by means of which the milling inserts are mounted, will consequently decrease in size. Small screws or other fastening members are difficult to handle since they easily are dropped in the mounting of the milling inserts. Small screws have also lower mechanical strength and are more difficult to screw in, since the threads and the screw head are more fragile and sensitive to the position of the screw in the threads. If the screw enters obliquely into the screw hole, the risk is great that the threads are destroyed, which has the consequence that the screw is destroyed. Also the threaded hole in the basic body may be damaged, which involves a great additional cost since the entire basic body may be needed to be replaced. For axially mounted milling inserts, it may also be hard to get access for tools when the milling inserts are to be mounted. Because of the diameter of the basic body, when small milling tools are concerned, also the number of milling inserts possible to mount becomes limited. Usually, the pitch is formed in such a way that one or two milling inserts are used simultaneously.
Tangentially mounted indexable milling inserts for milling cutters are disclosed in, for instance, U.S. Pat. No. 6,872,034 and U.S. Pat. No. 7,241,082, wherein the indexable milling insert is mounted by a through screw. By the fact that the milling inserts are mounted tangentially in the basic body, the problem to access the screw by the tool becomes smaller. However, the problem of milling cutters of small diameters (<25 mm diameter) remains, foremost the fact that the loose details become difficult to handle, as well as that small fastening members are sensitive in the mounting step and have lower mechanical strength.
The present invention aims at obviating the above-mentioned disadvantages of previously known indexable milling inserts and at providing an improved indexable milling insert. Therefore, a primary object of the invention is to provide indexable inserts, and milling tools having indexable milling inserts, that are suitable for small diameters (<25 mm).